In mobile communications networks, a handover refers to the switching from one communications channel to another communications channel during the progress of a call. Such switching may occur, for example, when a mobile subscriber moves out of range of one base station and into the range of another base station. Handover can also occur when a subscriber moves between antennas in the same base station.
In packet-based mobile communications networks, handovers must be performed not only on the radio interface, but also on the media gateway or gateways associated with the base stations involved in the handover. A media gateway is a network entity that switches media stream communications between its input and output ports and may translate the media stream from one format to another format. Media gateways do not participate in call signaling and consequently do not maintain call state information. A media gateway controller performs signaling functions to establish and tear down calls across media gateways. Thus, performing a handover in a media gateway can include sending commands to the media gateway from one communications channel to another communications channel and freeing resources used by the old channel.
The MEGACO protocol, as described in ITU-T Recommendation H.248, includes commands for establishing contexts in a media gateway. A context is analogous to a call or a communications session between one or more parties. In a media gateway, a context is defined by its endpoints, referred to as terminations. Typically, a context has two terminations in the media gateway—one for communications to and from one party and one for communications to and from another party.
One problem with providing handover support in some existing media gateways is that these media gateways utilize conference bridges to provide handover support. The conference bridge is used to establish the new communications channel to receive the call when the handover is performed. The new communications channel and the old communications channel exist simultaneously in the conference bridge. When a handover occurs, the conference bridge switches the call to the new communications channel and frees resources associated with the old communications channel. While using a conference bridge provides one solution for performing handover in a media gateway, conference bridges are expensive and are not scalable to meet increasing network demands.
Accordingly, in light of these difficulties associated with conventional media gateways and media gateway control protocols, there exists a need for improved methods and systems for providing handover support in a media gateway.